1. Field of Invention
This invention relates to circuitry for detecting peak levels of signals and particularly peak detectors for analyzing signals of generally arbitrary wave shape and form.
Peak signal detectors are widely known and useful circuit devices. A peak detector may be used as an AC signal to DC signal converter, as a demodulator or as a diagnostic tool.
Various circuit solutions have been suggested for providing peak signal indications. Among them are peak envelope detectors, sample and hold circuits and level sensing circuits. Known solutions have a wide variety of limitations and disadvantages, including limitations on large amplitude operating range and frequency range and inability to approach true peak level detection. What is needed is a peak detector which approaches true peak detection over a wide frequency range and large amplitude operating range.
2. Description of the Prior Art
FIG. 1 illustrates one example of a typical prior art peak detector. A signal applied to node 1 through a capacitor 2 is rectified by a diode 3 coupled between node 4 and a ground reference level causing a charge to develop across an integrating capacitor 5 thereby to raise the average voltage level at a node 6 toward a peak level relative to ground corresponding to the peak amplitude of the signal applied at node 1. A discharge resistor 8 may be provided across the integrating capacitor 5. The charge-discharge rate of the integrating capacitor 5 is a function of the time constant determined by the values of resistor 7 and 8 and integrating capacitor 5 modified by the on impedance and off impedance of the diode 3.
The circuit of FIG. 1 has numerous limitations typical of the prior art. For example, the time constants determining the charge and discharge rate of the integrating capacitor 5 tend to vary with the impedance of the diode 3, which in turn is affected by temperature and by input signal operating region. Further, the discharge time constant of the integrating capacitor 5 is such that the circuit is generally not capable of tracking dynamic variations in peak output over a wide frequency range. Such limitations render this type of detector unsuitable for high speed, high precision applications.